1009电影剪辑错误,没有意义

我正在制作一个游戏,最初我是手动将英雄电影放在舞台上。现在我将英雄添加到容器中,并将容器加载到Main.as构造函数中。

这行出现1009错误:

bulletOffset = 5 / _root.accuracy;

下面是英雄类的相关代码:

public class Hero extends MovieClip {

    private var radius:Number;

    //Bullet offset
    private var bulletOffset:Number;

    //Player variables
    private var walkingSpeed:int = 3;

    private var shootingRate:int = 120;

    private var s:int;

    //Making all of the items on the stage accessible by typing "_root.[ITEM]"
    private var _root:MovieClip;

    private var leftKeyDown:Boolean = false;
    private var upKeyDown:Boolean = false;
    private var rightKeyDown:Boolean = false;
    private var downKeyDown:Boolean = false;
    private var punchKeyDown:Boolean = false;

    //Player states (shooting, attacking etc)
    private var shooting:Boolean = false;

    public function Hero() 
    {
        addEventListener(Event.ADDED, beginClass);
    }

    private function beginClass(event:Event):void
    {

        //Determine the radius
        radius = this.width - 8;

        _root = MovieClip(root);

        bulletOffset = 5 / _root.accuracy;

             blablablabla